JPH09246929A - Actuator driving circuit provided with overcurrent protection function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To flexibly respond to non-uniform protection requests corresponding to the state of an overcurrent in an actuator driving circuit provided with a function for protecting the circuit from the overcurrent due to the short circuit of a load or the like together. SOLUTION: A driving element 2 is normally turned ON by a driving command (gate signal) GS added from a controller 10 and drives an actuator 1. A comparator 4, a charging/discharging switching circuit 5, an integration circuit 6 and a hysteresis comparator 7 constitute a variable timer circuit and variable timer time corresponding to a voltage value at each time, that is the overcurrent, is set to the timer circuit on condition that a load voltage VL exceeds a prescribed value. The timer time is set as the time until a charging voltage to the integration circuit 6 reaches the threshold value Vth1 of the hysteresis comparator 7, and at the time of reaching the timer time, the driving command GS is interrupted through an AND gate 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an actuator drive circuit for driving various actuators based on a drive command from a control device, and particularly has a function of protecting the circuit from an overcurrent caused by a load short circuit or the like. The present invention relates to an actuator drive circuit having an overcurrent protection function.

[0002]

2. Description of the Related Art Conventionally, an actuator drive circuit of this type having an overcurrent protection function is disclosed in, for example, Japanese Patent Laid-Open No. 2-3.
The circuit described in Japanese Patent No. 01802 is known.

By the way, in the circuit described in the above publication, when an overcurrent flows through the drive element (semiconductor switch) due to a short circuit of the load, the load voltage is largely changed, and therefore, in addition to the drive element. The drive command that is issued is cut off. By cutting off the drive command in this way, the drive element is turned off, and it is prevented that the drive element is destroyed.

However, in most of the above loads, an inrush current flows when the load is driven, and an overcurrent due to the inrush current flows for a short time immediately after the drive element is turned on. Then, when such an overcurrent flows, the load voltage also temporarily fluctuates greatly.Therefore, if the drive command is cut off simply by using the change in the load voltage as a trigger, erroneous protection is executed, and eventually There is a concern that the load will not start.

Therefore, the circuit disclosed in the above publication also includes a timer circuit (delay circuit) for delaying the interruption of the drive command for a fixed time during which the inrush current flows, and the drive command becomes active for a fixed period. Even if the load voltage changes, the cutoff of the drive command is prohibited.

By thus providing the timer circuit and prohibiting the drive command from being cut off for a certain period when the drive command becomes active, the erroneous protection operation due to the inrush current is preferably avoided. Become.

[0007]

By the way, although the load is short-circuited, the contents thereof are actually various. For example, in a fuel pump used in an internal combustion engine mounted on a vehicle, in addition to a short circuit due to a short circuit of wiring, In addition, there is also a pseudo short circuit called a so-called half lock in which an overcurrent state occurs due to the blockage of the fuel transfer path due to dust or the like. Then, in the case of this half-lock, normally, an overcurrent state is certainly brought about, but a current larger than that in the case of the short circuit due to the short circuit of the wiring does not flow.

On the other hand, in the case of a short circuit due to a short circuit of the wiring, it is desirable to turn off the drive element as early as possible in order to avoid the destruction, but in the case of the half lock, the drive element is destroyed. Depending on the content of the short circuit, the required protection content is not uniform, for example, it is desirable to maintain the drive state as much as possible so that the dust and the like can be flushed out and that the half lock state can be recovered early. . In particular, in the case of the in-vehicle actuator such as the fuel pump described above, such overcurrent protection content directly affects the running of the vehicle, so it is important to respond to the required protection content. It's a problem.

However, although the above-mentioned conventional drive circuit (load failure detection circuit) includes a timer circuit,
The timer time (delay time) is constant. Moreover, in the conventional drive circuit, the timer circuit does not operate after a certain period of time corresponding to the timer time has passed since the drive command was activated, that is, after the overcurrent caused by the inrush current flows. It is also accompanied. Therefore, if a short circuit occurs in the load after that, a protection operation that immediately interrupts the drive command is executed regardless of the content,
However, it has been impossible to meet the demand for protection that is not uniform according to the state of the overcurrent.

Conventionally, as an actuator drive circuit having such an overcurrent protection function, for example, a circuit described in Japanese Patent Laid-Open No. 64-64523 or Japanese Patent Laid-Open No. 3-4324.
There is also a circuit described in Japanese Patent Laid-Open No. 106114. However, none of these circuits has even the timer circuit (delay circuit), and the fact that it is not possible to meet the uneven protection demand depending on the state of the overcurrent is the same in the case of these circuits. Is the same.

The present invention has been made in view of the above circumstances, and provides an actuator drive circuit having an overcurrent protection function capable of flexibly responding to a protection request that is not uniform according to the state of the overcurrent. The purpose is to do.

[0012]

In order to achieve such an object, according to the present invention, according to the constitution of claim 1, (a) the load current exceeds a predetermined value, and the current value is adjusted according to the current value. A variable timer means in which a variable timer time is set. (B) Gate means for cutting off the drive command applied to the drive element on condition that the variable timer means reaches the timer time. Is basically provided to flexibly respond to the non-uniform protection request depending on the state of the overcurrent.

According to this structure, the timing at which the drive command is cut off is changed according to the timer time set in the variable timer means. The timer time set in the variable timer means is variably set according to the current value of the overcurrent when the load current exceeds a predetermined value, that is, when the overcurrent flows.

Therefore, for example, even in the above-described fuel pump for an on-vehicle internal combustion engine, when an extremely large overcurrent flows as a load current, such as a short circuit due to a short circuit of wiring, the same variable timer means is used. For example, a short timer time is set according to the current value. On the other hand, when an overcurrent smaller than this, such as the half lock, flows as the load current, a long timer time corresponding to the same current value is set in the variable timer means. If the timer time is set in the variable timer means in such a manner, respectively, As a result, the destruction and the like can be prevented appropriately. -When an overcurrent smaller than this, such as half lock, flows as the load current, the drive state is maintained to the extent that the drive element is not destroyed. Therefore, the possibility of early recovery from a half-locked state, such as easy flow of dust, increases. Above all, in a fuel pump of an internal combustion engine for a vehicle, the driving state of the fuel pump is maintained to the maximum extent, so that the traveling of the vehicle is not stopped unnecessarily. And so on, it becomes possible to flexibly meet the non-uniform protection demand depending on the state of the overcurrent.

According to the second aspect of the invention, (a1) the variable timer means is an integrating circuit in which when the extracted load current exceeds a predetermined value, an electric charge corresponding to the current value is charged. And a comparator which compares the output of the integrating circuit with a predetermined threshold value and outputs a timer-up signal when the output of the integrating circuit exceeds the threshold value. (B1) The gate means cuts off a drive command applied to the drive element based on a timer-up signal output from the comparator. With such a configuration, the timer time setting in the above-exemplified mode of the variable timer means can be easily and properly realized.

That is, in this case, the output of the integrator circuit reaches the threshold value earlier as the above-mentioned overcurrent becomes larger. As a result, the variable timer means has the above-mentioned magnitude of the overcurrent. The timer time having a length inversely proportional to this is set variably. In this way, by variably setting the timer time of a length that is inversely proportional to the magnitude of the overcurrent, it is possible to flexibly respond to the protection request that is not uniform according to the state (magnitude) of the overcurrent. What can be done is as described above.

On the other hand, according to the third aspect of the present invention, (a2) the variable timer means is charged with an electric charge corresponding to the current value when the extracted load current exceeds a predetermined value, and is extracted. When the load current is less than or equal to a predetermined value, the integrator circuit that discharges the charged electric charge and the output of the integrator circuit and the predetermined first and second threshold values are compared, and the output of the integrator circuit is the second A hysteresis comparator that outputs a timer-up signal when a first threshold value that is larger than the threshold value is output, and outputs a timer reset signal when the output of the integration circuit drops below the second threshold value. (B2) The gate means interrupts the drive command applied to the drive element based on the timer up signal output from the hysteresis comparator, and releases the drive command interrupted based on the timer reset signal.
According to such a configuration, in addition to the realization of the timer time setting in the above-exemplified mode of the variable timer means, the driving element is driven every time its output falls below the second threshold value due to the discharge of the integrating circuit. It will be driven again.

That is, even if a short circuit or a half lock occurs due to the above-mentioned short circuit of the wiring, the re-driving is repeated in this manner, so that the load is given an opportunity to be returned to the normal condition. In particular, for an actuator that directly affects the traveling of the vehicle such as the fuel pump, such consideration becomes extremely significant.

At this time, in the above integrating circuit,
At least during the discharging, charging due to the overcurrent is stopped (the driving of the load itself is stopped during the synchronization), so that the output once reaches the first threshold value, It falls to the second threshold value with a constant time constant regardless of the magnitude of the overcurrent. Therefore, even if the first threshold value is reached early due to a large overcurrent, the time until the driving element is re-driven, that is, the off-timer time is not unnecessarily shortened.

Further, in the structure of the invention described in claim 3, as in the invention described in claim 4, the time constant for charging / discharging the integrating circuit is such that charge time constant <discharge time constant. By setting to (4), such an off-timer time is preferably extended, and more stable re-driving of the driving element is realized.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of an actuator drive circuit having an overcurrent protection function according to the present invention.

The circuit of this embodiment is, for example, in the fuel pump drive circuit for an on-vehicle internal combustion engine described above, and when an overcurrent resulting from a short circuit due to a short circuit of the wiring or a half lock flows in the load, It is configured as a circuit that protects a drive element such as a power transistor.

First, the configuration of the circuit according to this embodiment will be described in detail with reference to FIG. In such a drive circuit, a drive signal 2 such as a power transistor is normally turned on by inputting a gate signal GS as a drive command from a control device 10 such as an engine control device, and a pump motor 1 that is a load is driven.

However, in the above fuel pump and the like, as described above, a pseudo current in which an overcurrent state is caused due to a short circuit due to a short circuit of wiring or a blockage of a fuel transfer path due to dust called half lock. A short circuit may occur. If such a state is maintained, the drive element 2 may be destroyed.

On the other hand, even in the same overcurrent state, in the case of a short circuit due to the short circuit of the wiring, it is desirable to turn off the driving element 2 as early as possible in order to avoid the destruction thereof. In the case of the half lock, it is desirable to maintain the drive state as much as possible so that the drive element 2 is not destroyed, in order to flush the dust and the like and to recover the half lock state early. As mentioned above, the required protection contents are not uniform. In particular, in the case of the above-described fuel pump and other vehicle-mounted actuators, the protection content against such overcurrent will directly affect the running of the vehicle. Therefore, how to deal with the required protection content. Has become an important issue.

Therefore, in the circuit of this embodiment, as shown in FIG. 1, a shunt resistor 3 is provided between the output terminal of the driving element 2 and the ground, and the load current is monitored through the voltage VL generated there. And the comparator 4,
The charge / discharge switching circuit 5, the integrating circuit 6, and the hysteresis comparator 7 constitute a variable timer circuit so that different timer times can be variably set in the timer circuit according to the magnitude of the overcurrent flowing through the load. And
When the timer time variably set in the timer circuit is reached, the drive command (gate signal) GS is cut off through the AND gate 8 so that the drive signal DS is not applied to the drive element 2.

The specific configuration and function of each of these circuits that make up the variable timer circuit will be sequentially described below. First, the comparator 4 is a circuit that monitors whether the load current is in an overcurrent state. This circuit 4
It is configured to have a comparator 41 to which a voltage VL corresponding to the load current is applied to a non-inverting input and a determination voltage Vref for determining an overcurrent state is applied to an inverting input. This judgment result is added to the charge / discharge switching circuit 5.

The charging / discharging switching circuit 5 is a circuit for switching the charging / discharging operation of the integrating circuit 6 in the subsequent stage according to the result of the judgment by the comparator 4 as to whether or not it is in the overcurrent state. The circuit 5 is judged by the comparator 4 to be in the overcurrent state, that is, the transistor 51 which is turned on only during the period in which VL> Vref, and the comparator 4 to judge that the circuit 5 is not in the overcurrent state. The transistor 52 is turned on for a period, that is, a period of VL ≤ Vref. According to the charge / discharge switching circuit 5, when the transistor 51 is turned on, the voltage VL directly corresponding to the magnitude of the overcurrent is taken into the integrating circuit 6 as it is, and the capacitor 61 is charged. It will be accumulated.

The integrating circuit 6 basically comprises a capacitor 61.
And a resistor 62, which is a CR integrator circuit. Therefore, the charging time constant basically also has a time constant CR1 corresponding to those element constants. However, the rise of the output voltage when the transistor 51 is on depends on the taken-in voltage. It will be different depending on the VL. That is, the higher the voltage VL (the larger the overcurrent), the faster the output voltage of the integrating circuit 6 rises, and the lower the voltage VL (the smaller the overcurrent), the more gently the output voltage of the integrating circuit 6 rises.

On the other hand, in the integrating circuit 6, at the time of discharging when the transistor 52 is turned on, the electric charge charged in the capacitor 61 is discharged through the resistor 62 and the resistor 63. That is, at this time, the charge stored in the capacitor 61 is C (R1 + R2).
With such a time constant, discharge is performed at a constant speed regardless of the magnitude of the overcurrent.

In this variable timer circuit, the hysteresis comparator 7 has the first threshold voltage Vth1.
And a second threshold voltage Vth2 that is smaller than the first threshold voltage Vth1, and compares the output voltage of the integration circuit 6 with the first and second threshold voltages Vth1 and Vth2. It is a circuit that forms a timer-up signal and a timer-reset signal based on the above.

That is, the same circuit 7 is provided in the first or second circuit.
Threshold voltage Vth1 and Vth2 are applied to the non-inverting input, and the output voltage of the integrating circuit 6 is applied to the inverting input. And a voltage divider circuit (resistors 72, 73 and 75) in which the first and second threshold voltages Vth1 and Vth2 are switched and set. With the charging / discharging operation of the integrating circuit 6, When the output voltage of the integrating circuit 6 reaches the first threshold voltage Vth1, the output CS outputs a timer-up signal that is inverted from a logic high level to a logic low level. At this time, the transistor 74 is turned on as the output CS becomes a logic low level, and the threshold voltage of the comparator 71 is switched to the second threshold voltage Vth2. On the other hand, the output voltage of the integrating circuit 6 is the second threshold voltage Vth.
When it falls below 2, the output CS outputs a timer reset signal which is inverted from a logic low level to a logic high level. At this time, the transistor 74 is turned off as the output CS becomes a logic high level,
The threshold voltage of the comparator 71 switches to the first threshold voltage Vth1. Such an operation is repeatedly executed.

Since such an operation is executed in the hysteresis comparator 7, in the variable timer circuit, the transistor 5 of the charge / discharge switching circuit 5 is eventually obtained.
1 is turned on and the charging operation of the integration circuit 6 is started until the timer up signal is output is the on timer time, and the transistor 5 of the charge / discharge switching circuit 5 is
The off-timer time is from the time when 2 is turned on and the discharge operation of the integrating circuit 6 is started until the timer reset signal is output. Of these, only the on-timer time is variably set according to the magnitude of the monitored overcurrent. As described above, the gate signal GS is cut off through the AND gate 8 when the variably set timer time, that is, the ON timer time is reached.

Now, let us consider specifically how and to what extent the on-timer time is variably set in this variable timer circuit. First, let us consider how the on-timer time is variably set when no charge is stored in the capacitor 61 forming the integration circuit 6.

In the integrating circuit 6 having the time constant CR1, when the input voltage is Vin, the input voltage Vi
The current flowing through the circuit when n is added is i = (Vin × e ^ (-t / CR1)) / R1 (1), where i is the current. Here, “^ ()” represents exponentiation.

Therefore, when the output voltage of the integrator circuit 6 is Vout, Vout = Vin (1-e ^ (-t / CR1)) (2), and the change of the output voltage Vout with time, that is, It can be seen that the slope depends on the magnitude of the input voltage Vin.

At this time, when the output voltage Vout reaches the first threshold voltage Vth1 of the hysteresis comparator 7, that is, the on-timer time is T, then T = -CR1 × log (1-Vth1 / Vin) (3) At this time, the input voltage Vin is equal to the voltage VL.
Since it is considered to be almost equal to (voltage corresponding to the amount of overcurrent of the load), the equation (3) can also be expressed as T = −CR1 × log (1-Vth1 / VL) (3) ′.

On the other hand, the time constant C (R
1 + R2), discharge is performed, and immediately after the off-timer time has passed, that is, charge is performed again from the state where the charge CVth2 corresponding to the second threshold voltage Vth2 of the hysteresis comparator 7 is stored in the capacitor 61. Then, when the input voltage Vin is applied, the current i flowing in the circuit is i = (Vin-Vth2) * e ^ (-t / CR1)) / R1 (4).

Therefore, in this case, the output voltage Vout of the integrating circuit 6 is Vout = Vin (1-e ^ (-t / CR1)) + Vth2 × e ^ (-t / CR1) (5) It can be seen that the change, that is, the slope, of the voltage Vout with time also depends on the magnitude of the input voltage Vin.

At this time, the time taken for the output voltage Vout to reach the first threshold voltage Vth1 of the hysteresis comparator 7, that is, the on-timer time, is T = -CR1 * log {(Vin-Vth1). / (Vin-Vth2) (6) Again, since the input voltage Vin is considered to be substantially equal to the voltage VL, the equation (6) is expressed as T = −CR1 × log {(VL-Vth1) / (VL-Vth2) ... (6) ′. Will be done.

In the variable timer circuit, as described above, the on-timer time is variable according to the voltage VL, that is, the magnitude of the overcurrent, regardless of whether or not the charge is stored in the capacitor 61 forming the integrating circuit 6. Will be set.

Next, how much the on-timer time is variably set in the variable timer circuit will be considered. It has been described above that the on-timer time T is set according to the equation (3) or the equation (3) ′ when there is no charge stored in the capacitor 61.

When the first threshold voltage Vth1 is, for example, Vth1 = 2.00 [V], the voltage VL corresponding to the overcurrent flowing when the short circuit occurs due to the short circuit of the wiring is, for example, VL = 12.00 [V], and in the pseudo short circuit due to the half lock, the voltage VL corresponding to the overcurrent flowing therethrough is, for example, VL = 5.00 [V] or = 4.00 [V] or = Assuming 3.00 [V] or = 2.01 [V], the ratio of the on-timer time T at the time of a short circuit due to the short circuit of the wiring and the on-timer time T at the time of a pseudo short circuit due to the half lock is the above ( By the formula 3) ′, when the voltage VL at the time of half lock is 5.00 [V] → 2.8 times 4.00 [V] → 3.8 times 3.00 [V] → 6. 0 times 2.01 [V] Can → 29.1 times become.

In the variable timer circuit,
The on-timer time greatly changes according to the voltage VL (the magnitude of the overcurrent). When the voltage VL is slightly higher than the threshold voltage Vth1 during the half lock, that is, when the voltage VL is in the range of 2.00 <VL <2.01, the on-time is set. The time T is 30 times or more than that at the time of a short circuit due to the short circuit of the wiring, but the driving element 2 is not destroyed by such a small overcurrent state.

On the other hand, when the capacitor 61 is charged again from the state where the electric charge CVth2 corresponding to the second threshold voltage Vth2 of the hysteresis comparator 7 is stored, that is, when the continuous charging operation is performed,
The on-timer time T is set according to the equation (6) or the equation (6) ′ as described above.

Here, the first and second threshold voltages Vt
When h1 and Vth2 are, for example, Vth1 = 2.00 [V] Vth2 = 0.50 [V], the voltage VL corresponding to the overcurrent flowing therethrough is short-circuited when the wiring is short-circuited. VL = 12.00 [V], and at the time of the pseudo short circuit due to the half lock, the voltage VL corresponding to the flowing overcurrent is VL = 5.00 [V] or = 4.00 [V] or = Assuming 3.00 [V] or = 2.01 [V], the ratio of the on-timer time T at the time of a short circuit due to the short circuit of the wiring and the on-timer time T at the time of a pseudo short circuit due to the half lock is the above ( 6) ′ expression, when the voltage VL at half lock is 5.00 [V] → 2.9 times 4.00 [V] → 4.0 times 3.00 [V] → 6. 6 times 2.01 [V] When → 35.9 times become.

Incidentally, the ratio of the on-timer time T when the electric charge is not stored in the previous capacitor 61 and the on-timer time T when the electric charge CVth2 corresponding to the second threshold voltage Vth2 is stored is the above. It is 1.3 times that under the condition of Vth2 = 0.50 [V]. When it is desired to reduce this ratio, the second threshold voltage Vth2 may be set to a lower voltage. By setting the second threshold voltage Vth2 to Vth2 = 0 [V], the ratio becomes 1 That is, they have the same on-timer time.

In any case, according to this variable timer circuit, it is understood that the on-timer time greatly changes according to the voltage VL (the magnitude of the overcurrent). FIG.
3 and FIG. 3 respectively show an operation example of the drive circuit of the same embodiment including such a variable timer circuit. Next, referring to FIGS. 2 and 3 together, the circuit of the same embodiment will be described. The overcurrent protection operation will be described in more detail.

First, with reference to FIG. 2, what kind of protection operation is performed by the circuit of this embodiment at the time of short circuit due to the short circuit of the wiring and at the time of pseudo short circuit due to the half lock or the like will be described. .

In FIG. 2, FIG. 2A shows a gate signal (drive command) G applied from the controller 10.
2B shows the transition of S, and FIG. 2B shows the transition of the drive signal DS which is the output of the AND gate 8. Further, FIG. 2C shows a transition of the voltage VL corresponding to the load current, and FIGS. 2D and 2E respectively show the integrating circuit 6
3 shows the transition of the input voltage (Vin) and the output voltage (Vout) of the. Then, FIG. 2F shows the transition of the logic level of the output CS of the hysteresis comparator 7 which becomes the timer up signal or the timer reset signal.

Now, assuming that the output CS of the hysteresis comparator 7 is at a logic high level, as shown in FIG.
If the application of the gate signal GS from the control device 10 is started at the time t11 in the mode shown in FIG.
The AND condition at AND gate 8 is established in 11 and FIG.
In the mode shown in (b), the drive signal DS is applied to the drive element 2. The drive element 2 is thus driven by the drive signal DS
Is turned on by the addition of, and at the same time t11, driving of the motor 1, which is a load, is started.

Since a rush current normally flows through the motor 1 at the start of its drive, the voltage fluctuation caused by the rush current is also applied to the load voltage VL in the manner shown in FIG. 2 (c). Will occur. If the changed voltage VL exceeds the determination voltage Vref, the comparator 4 determines that the overcurrent state is present,
Only when the voltage VL exceeds the determination voltage Vref, the transistor 51 of the charge / discharge switching circuit 5 is turned on. Therefore, also in the integrator circuit 6, the input voltage is generated in the manner shown in FIG. 2D, but the discharge operation is immediately switched to, so that the output voltage is changed to that in FIG. ), It decays immediately. That is, in the circuit of the same embodiment, the overcurrent generated due to such an inrush current is preferably ignored.

However, after that, at time t12, if a short circuit due to the short circuit of the wiring occurs for some reason, the voltage VL becomes large due to the large overcurrent.
It rapidly increases in the manner shown in FIG.

When such an overcurrent occurs,
In the circuit of the embodiment, as described above, the comparator 4 determines that an overcurrent has occurred, that is, that the voltage VL exceeds the determination voltage Vref. -As a result, the transistor 51 of the charge / discharge switching circuit 5 is turned on. 2D, the voltage VL is input to the integrator circuit 6, and the charging voltage of the integrator circuit 6 is changed from the integrator circuit 6 in the manner shown in FIG. 2E. It will be output.

At this time, the output voltage of the integrator circuit 6 changes according to the level (the magnitude of the overcurrent) of the voltage VL, which is the input voltage, as expressed by the equation (2), and It has also been described above that the first threshold voltage Vth1 of the hysteresis comparator 7 is reached in a time period calculated based on the equation (3) or the equation (3) ′. In this example, after the overcurrent is detected at the time t12, the output voltage of the integrating circuit 6 reaches the first threshold voltage Vth1 at the time t13. That is, in this case,
The on-timer time is a short time corresponding to (time t13-time t12), as also shown in FIG. 2 (e).

Thus, at time t13, the first threshold voltage V
When th1 is reached, in the circuit of the embodiment, the timer up signal is output from the hysteresis comparator 7 in the mode shown in FIG. 2 (f). That is, the output CS of the hysteresis comparator 7 is inverted from the logic high level to the logic low level.

As a result, the AND condition is not satisfied in the AND gate 8 and the drive element 2 is driven in the mode shown in FIG. 2B even though the gate signal GS is held. The applied drive signal DS is cut off. That is, the energization to the drive element 2 is stopped in the mode shown in FIG. 2C, and the protection is achieved.

On the other hand, by outputting the timer-up signal in this way, in the hysteresis comparator 7, the transistor 74 is turned on, and the threshold value of the second threshold voltage Vth1 is lower than the second threshold voltage Vth1.
Is changed to the threshold voltage Vth2. In the circuit of the embodiment, the first and second threshold voltages Vth1 and Vth
It is assumed that the relationship of th2 is as shown in FIG. And, by the comparator 4, the voltage VL
Is determined to be equal to or lower than the determination voltage Vref (at this point, the energization of the drive element 2 is stopped). -As a result, the transistor 52 of the charge / discharge switching circuit 5 is turned on. 2 (e), the discharging operation of the integrating circuit 6 is started, and the output voltage thereof becomes equal to or lower than the changed second threshold voltage Vth2, as shown in FIG. In the mode shown in (f), the timer reset signal is output from the hysteresis comparator 7. That is, the output CS of the hysteresis comparator 7 is inverted from the logic low level to the logic high level again. In this example, after the discharging operation of the integrating circuit 6 is started at the time t13, the output voltage becomes equal to or lower than the second threshold voltage Vth2 at the time t14, and such logic level inversion is performed.

When the output CS of the hysteresis comparator 7 becomes a logic high level in this way, the first threshold voltage Vth1 is again selected as the threshold value,
Also in the AND gate 8, the AND condition with the held gate signal GS is satisfied again, and FIG.
In the mode shown in, the cutoff of the drive signal DS is released.

Then, if (time t14-time t13)
If the normal state is restored from the short-circuited state due to the wiring short-circuiting or the like while the off-timer time corresponding to such time elapses, the motor 1 driven by the drive element 2 in the mode shown in FIG. The drive is restarted.

On the other hand, if a half lock occurs at time t15 after that due to the blockage of the fuel transfer path due to the above-mentioned dust and the like, even though it is an overcurrent, a current smaller than that at the time of the previous wiring short circuit causes The voltage VL is as shown in FIG.
It slightly increases in the mode shown in (c).

Even when such an overcurrent occurs, in the circuit of the embodiment, the fact that the overcurrent is generated by the comparator 4, that is, the same voltage VL exceeds the judgment voltage Vref. It is determined that -As a result, the transistor 51 of the charge / discharge switching circuit 5 is turned on. 2D, the voltage VL is input to the integrator circuit 6, and the charge voltage is output from the integrator circuit 6 in the manner shown in FIG. 2E. Become so.

Also at this time, the output voltage of the integrator circuit 6 changes according to the level (the magnitude of the overcurrent) of the voltage VL, which is the input voltage, according to the equation (2). In addition, the first threshold voltage Vth1 of the hysteresis comparator 7 is reached in the time obtained based on the above equation (3) or equation (3) '.

That is, in the half-lock state where the overcurrent is relatively small, the output voltage of the integrating circuit 6 is the same as that shown in FIG.
As shown in (e), it rises relatively slowly, and reaches the first threshold voltage Vth1 after a longer ON timer time. In this example, after the overcurrent is detected at the time t15, the output voltage of the integration circuit 6 reaches the first threshold voltage Vth1 at the time t16. That is, in this case, the on-timer time is a relatively long time corresponding to (time t16-time t15).

After the output voltage of the integrator circuit 6 reaches the first threshold voltage Vth1 in this way, the same as the above is given: -The timer up signal is output from the hysteresis comparator 7 in the mode shown in FIG. 2 (f). It That is,
The output CS of the hysteresis comparator 7 is inverted from the logic high level to the logic low level. By this, the AND condition is not satisfied in the AND gate 8 and the AND signal is applied to the drive element 2 in the mode shown in FIG. 2B even though the gate signal GS is held. The drive signal DS is cut off. On the other hand, by outputting the timer-up signal in this way, in the hysteresis comparator 7, the transistor 74 is turned on, and the threshold value is changed from the first threshold voltage Vth1 to the second threshold voltage Vth2. It When the discharge operation of the integration circuit 6 is started based on the transistor 52 of the charge / discharge switching circuit 5 being turned on, and the output voltage thereof becomes the second threshold voltage Vth2 or less, as shown in FIG. 2 (f). In this manner, the hysteresis reset signal is output from the hysteresis comparator 7. That is, the output CS of the hysteresis comparator 7 returns to the logical high level. A series of operations such as will be executed. In the example here, the integration circuit 6 is operated at the time t16.
After the discharge operation is started, the output voltage becomes equal to or lower than the second threshold voltage Vth2 at time t17, and such logic level inversion is performed.

When the output CS of the hysteresis comparator 7 becomes a logical high level in this way, the threshold value of the first threshold voltage Vth1 is again set in the same manner.
Is selected, and also in the AND gate 8, the AND condition with the held gate signal GS is satisfied again, and the cutoff of the drive signal DS is released.

As described above, in the circuit of the present embodiment, the ON timer times of different lengths are variably set according to the magnitude of the overcurrent. Therefore, in order to avoid damage to the driving element 2 when a large overcurrent flows, such as a short circuit due to a short circuit in the wiring,
I want to turn this off as early as possible. When the overcurrent is relatively small, such as a pseudo short circuit due to half-lock, dust or the like flows, and as a result, the drive element 2 is driven as much as possible so that the drive element 2 is not destroyed so that the half-lock state can be recovered early. Want to keep And so on, it becomes possible to suitably deal with the protection requirement which is not uniform depending on the contents of the short circuit.

Next, referring to FIG. 3, the half lock or the like occurs during the high load operation of the motor 1, and thereafter,
When the short circuit of the wiring, the half lock, etc. are repeated without being restored to the normal state, mainly the behavior of the variable timer circuit of the circuit of the embodiment will be described for reference.

In FIG. 3A as well, FIG. 3A shows a gate signal (drive command) GS applied from the controller 10.
3B, and FIG. 3B shows the transition of the drive signal DS which is the output of the AND gate 8. FIG.
3C shows the transition of the voltage VL corresponding to the load current, and FIGS. 3D and 3E respectively show the integrating circuit 6
3 shows the transition of the input voltage (Vin) and the output voltage (Vout) of the. Similarly, FIG. 3 (f) also shows the transition of the logic level of the output CS of the hysteresis comparator 7 which becomes the timer up signal or the timer reset signal.

Now, as shown in FIG.
It is initially assumed that after the driving of the motor 1, which is a load, is started at time t21, the driving of the motor 1 in the high load state is maintained, and that the motor 1 falls into the half lock state at time t22.

At first glance, it seems that an operation equivalent to that of the circuit of the above-described embodiment can be realized even by a normal timer circuit having an integrating circuit for preventing malfunction due to noise or the like. However, in such a normal timer circuit, when such a high load state is maintained, the charge (integral) level reaches a certain level, and then the above half lock or the like occurs. In some cases, it may not be possible to secure a sufficient on-timer time to recover from this state.

In this respect, in the circuit of the embodiment, as described above, the judgment voltage Vre is calculated in the comparator 4.
Since the charging operation of the integrating circuit 6 is started on the condition that the load voltage VL exceeding f is detected, the voltage VL determines the judgment voltage Vref even if such a high load state is maintained. As long as it does not exceed the limit, the charging operation is not performed in the integrating circuit 6.

For this reason, even if a half-lock state is entered at time t22 while maintaining such a high load state, as shown in FIG. 3 (e), it depends on the magnitude of the overcurrent at that time. In addition, a sufficient on-timer time (time t23-time t22) is secured.

On the other hand, as shown by the signal transition after time t23 in FIG. 3, despite such protection operation,
Even if the detection of the wiring short circuit or the half lock is repeated thereafter, according to the circuit of the embodiment, the constant off timer time (time t24-time t23,
Alternatively, the next power supply is not started until the time t26-time t25) has passed. The on-timer time (time t25-time t24, or time t27-time t26) that is variably set at that time is always in accordance with the magnitude of the overcurrent at that time, that is, in response to the uneven protection request. It will be an appropriate time.

As described above, according to the actuator drive circuit having the overcurrent protection function according to the embodiment, (a) the on-timer time of different length is variably set according to the magnitude of the overcurrent. Therefore, for example, when a large overcurrent flows, such as a short circuit due to a short circuit of wiring, in order to avoid destruction of the driving element 2,
I want to turn this off as early as possible. When the overcurrent is relatively small, such as a pseudo short circuit due to half-lock, dust or the like flows, and as a result, the drive element 2 is driven as much as possible so that the drive element 2 is not destroyed so that the half-lock state can be recovered early. Want to keep And so on, it becomes possible to suitably deal with the protection requirement which is not uniform depending on the contents of the short circuit. (B) Further, the off-timer time is set to a constant time independent of the on-timer time, so that the time until the driving element 2 is re-driven is not unnecessarily shortened. (C) Furthermore, by setting the time constant for charging / discharging the integrating circuit 6 to the relationship of charging time constant CR1 <discharging time constant C (R1 + R2), such an off-timer time is also appropriately extended and the above-mentioned driving is performed. It is also possible to realize more stable re-driving of the device 2. Many excellent effects can be achieved.

In the drive circuit of the above embodiment, the case where the circuit according to the present invention is applied to the circuit for driving the fuel pump of the on-vehicle internal combustion engine is shown, but a plurality of different overcurrent states are expected. As long as it has an actuator, the circuit of the present invention can be similarly applied to circuits for driving other actuators regardless of whether it is mounted on a vehicle, such as various solenoid drive circuits.

Further, in the circuit of the embodiment, since the drive circuit for the on-vehicle actuator is assumed, the timer circuit is once reset after the off-timer time has elapsed, and the actuators are restarted. However, when the drive circuit of the present invention is applied to an actuator that does not require restarting, at least the timer circuit is not automatically reset, that is, the on-timer time that is variably set as described above. It is also possible to adopt a configuration in which the subsequent energization to the drive element is stopped with the passage of time.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an actuator drive circuit having an overcurrent protection function according to the present invention.

FIG. 2 is a time chart showing an example of overcurrent protection operation of the circuit of the same embodiment.

FIG. 3 is a time chart showing an example of overcurrent protection operation of the circuit of the same embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Actuator (motor), 2 ... Drive element, 3 ... Shunt resistance, 4 ... Comparator, 5 ... Charge / discharge switching circuit, 6 ... Integration circuit, 7 ... Hysteresis comparator, 8
... AND gate, 10 ... Control device, 41, 71 ... Comparator, 51, 52, 74 ... Transistor, 61 ... Capacitor, 62, 63, 72, 73, 75 ... Resistor.

Claims (4)

[Claims] 1. A drive element for driving an actuator based on a drive command, a load current extracting means for extracting a current flowing in a load, and a current value corresponding to these current values provided that the extracted current exceeds a predetermined value. An overcurrent protection function comprising: variable timer means for setting a variable timer time; and gate means for interrupting a drive command applied to the drive element on condition that the variable timer means reaches the timer time. Actuator drive circuit. 2. The variable timer means, when the current extracted by the load current extracting means exceeds a predetermined value, an integrating circuit charged with electric charges corresponding to the current value, and an output of the integrating circuit and a predetermined value. And a comparator that outputs a timer-up signal when the output of the integrating circuit exceeds the threshold, the gate means is configured to output the timer-up signal based on the timer-up signal output from the comparator. The actuator drive circuit having an overcurrent protection function according to claim 1, which interrupts a drive command applied to the drive element. 3. The variable timer means is charged with a charge corresponding to the current value when the current extracted by the load current extracting means exceeds a predetermined value, and the extracted current becomes a predetermined value or less. At this time, an integrator circuit that discharges the charged electric charge is compared with an output of the integrator circuit and predetermined first and second threshold values, and a first threshold value in which the output of the integrator circuit is larger than the second threshold value. And a hysteresis comparator that outputs a timer-up signal when the output of the integrator circuit falls below a second threshold value, and the gate means outputs from the hysteresis comparator. The cutoff of the drive command applied to the drive element based on the timer up signal is canceled, and the cutoff of the drive command is released based on the timer reset signal. An actuator drive circuit having the described overcurrent protection function. 4. An actuator drive circuit having an overcurrent protection function according to claim 3, wherein the integration circuit is set such that the time constant for charging and discharging is such that charge time constant <discharge time constant.